1. Field of the Invention
The present invention relates to a steering system for vehicles of the type in which a rear wheel is steerable in relation to the steering operation of a front wheel.
2. Description of Revelent Art
There has already been proposed a steering system for vehicles in which a rear wheel is steerable in relation to the steering of a front wheel such that the steered angle ratio of the rear wheel to the front wheel is variable in accordance with the vehicle speed. (Japanese Laid Open Application No. JP-A-59-26363 dated Feb. 10, 1984).
More particularly, in this steering system, the rear wheel is steered, at relatively low vehicle speeds, in the opposite direction to the front wheel or substantially at an angle of zero degree and, at relatively high vehicle speeds, in the same direction as the front wheel. The steered angle ratio is given as a continuous function of the vehicle speed, as represented by a curve X shown in FIG. 11 of the accompanying drawings, such that for vehicle speeds higher than a predetermined vehicle speed d.sub.1 the steered angle ratio is positive, that is, the front and rear steered angles are the same in phase, and for vehicle speeds lower than the predetermined vehicle speed d.sub.1 the steered angle ratio is negative, that is, the steered angles are opposite in phase. In this manner, continuous control of the steered angle ratio is achieved to be effected along the function curve X, ranging from a low speed to a high speed. As a result, at relatively low vehicle speeds, the minimum turning radius of the vehicle as well as the inside wheel span is remarkably reduced, in addition to favorable vehicle turning characteristics such as when parking, travelling along a narrow curved road, and making a U-turn. Moreover, at relatively high vehicle speeds, the steering responsiveness can be highly improved.
Incidentally, in such steering system, in order to determine a proper possible steered angle ratio to be set in accordance with a signal corresponding to the vehicle speed, the speed the vehicle actually has is directly detected by a speed sensor as a signal source. However, in general, speed sensors available for such application tend to be complex in structure and consume an inordinate amount of space for installation, thus being disadvantageous in maintenance and cost effect. Moreover, in the case of a speed sensor with a continuous analog output, there may be required an additional element suc as an electric circuit for converting the analog output into a signal processable in a computer system for providing control.
With such point in mind, the present invention has been achieved to provide an improved in steering system for vehicles of the above-mentioned type.